1. Field of Invention
The present invention relates to a semiconductor device and a method of forming the same, and more generally to a semiconductor device including a polysilicon resistor and/or a polysilicon fuse and a MOS transistor having a metal gate and a method of forming the same.
2. Description of Related Art
As the dimension of a semiconductor device is getting smaller, the dimension of the gate structure and the thickness of the gate insulation layer are reduced accordingly. However, a leakage current occurs when the gate insulation layer of silicon oxide becomes thinner. To reduce the leakage current, a high dielectric constant (high-k) material is used to replace silicon oxide for forming the gate insulation layer. When the high-k material serves as the material of the gate insulation layer, the gate of polysilicon may react with the high-k material to generate a Fermi-level pinning, so as to increase the threshold voltage and affect the performance of the device. Therefore, a metal gate is used instead of a polysilicon gate nowadays.
As described above, when the polysilicon gate is replaced by the metal gate, the polysilicon layer of a resistor or a fuse structure in the semiconductor device is also replaced by the metal layer. The resistor and the fuse are required to have higher resistance based on the IC design requirement. However, since the polysilicon layer of the resistor or the fuse structure in the semiconductor device is replaced by the metal layer, the resistance of the resistor and the fuse is not high enough.